Interconnect (RC) delay is known to be a major limiting factor in the drive to improve the speed and performance of integrated circuits (ICs). For performance and cost reasons, it is desirable to have adjacent conductors as close as possible to one another. Since interconnect delay depends on both the dielectric constant of the insulating material that separates the interconnect conductors and the thickness of this insulating material, the interconnect delay can be reduced by using low dielectric constant materials such as ultra low-k (ULK) dielectric materials. Low-k dielectric materials refer to those insulating materials that have a dielectric constant (k) lower than that of silicon dioxide (SiO2) (k=3.9) and generally having k<=3. Ultra low-k dielectric materials generally have k-values less than about 2.6.
An important class of low-k and ULK dielectric materials is referred to as substitution-group depleted silicon oxide. By way of definition, these low-k and ULK materials have the chemical formula R1R2SiOx, where R1 and R2 refer to a hydrocarbon group such as a methyl group, an ethyl group, or a phenyl group or hydrogen. Such organo-silicate low-k and ULK dielectric films (organo-silicate glass=OSG) provide dielectric constants as low as about 2.0.
When the surface of OSG is exposed to oxidative or reductive reactive species such as are found in plasmas used to etch the OSG and used to remove (ash) resist patterns from the OSG, R1 and R2 groups may be removed from the OSG and replaced with O, OH, H or a dangling bond. When this occurs (often referred to as carbon depletion of OSG) it raises the dielectric constant and reduces the structural integrity of the OSG film. ULK dielectric films are more susceptible to plasma damage than low-k films.
It was discovered as described by Jiang et. al. in U.S. Pat. No. 7,741,224 hereby incorporated in its entirety for reference that performing a hydrocarbon plasma treatment of low-k and ULK dielectric films post etch and/or post ash can partially repair the damaged OSG and partially recover the dielectric constant.
As shown in the cumulative probability plot in FIG. 1 the dielectric constant (k) of an ultra-low-k OSG film as deposited 103 may be between 2.5 and 2.6. After an etch process 100 followed by a resist removal (ash) process 104 as illustrated in FIG. 2, damage to the exposed ULK surface caused by reactive species in the plasmas may raise the k value to 2.9 or greater (graph 105 in FIG. 1).
Performing a hydrocarbon plasma treatment 106 post ash 104 as is illustrated in FIG. 3, can repair some of the plasma damage and reduce the k value of the low-k film by about 1 unit as shown by the graph 107 in FIG. 1.
Unfortunately the dielectric constant of the low-k OSG is still significantly higher (median value ˜2.87) than the dielectric constant of the low-k OSG film as deposited (median value ˜2.55).